Cutaneous T-Cell Lymphoma and Microbiota: Etiopathogenesis and Potential New Therapeutic Targets

Objective To review the scientific literature related to human microbiota and cutaneous T-cell lymphoma. Methodology. An exploratory and systematic review of the articles retrieved from the bibliographic databases MEDLINE (PubMed), Embase, The Cochrane Library, and Scopus, published in the last 10 years with the following descriptors: “lymphoma, T-cell, cutaneous,” “microbiota,” “Mycosis Fungoides,” “Sézary Syndrome,” “lymphoma, primary cutaneous anaplastic large cell,” “Lymphomatoid Papulosis” and “Microbiota,” “microbiota,” “Microbial Community,” and “Microbial Communities.” Results Of the 87 references retrieved, after applying the inclusion and exclusion criteria, 21 articles were selected. Most studies linking cutaneous T-cell lymphoma and the microbiota focus on the cutaneous microbiome, with Staphylococcus aureus being the main related agent. Skin colonization by this bacterium could be involved in the hyperactivation of the STAT3 inflammatory pathway and in the overproduction of IL-17, both of which are widely related to the development of more aggressive and advanced forms of cutaneous T-cell lymphoma. We also found evidence of a possible relationship between intestinal dysbiosis and the development of cutaneous T-cell lymphoma, observing a decrease in taxonomic variability and an increase in certain genera such as Prevotella in the intestinal microbiome of patients with cutaneous T-cell lymphoma. The possible etiopathogenic mechanism underlying this relationship could be explained by an increase in systemic cytokine release, promoting the hyperactivation of STAT3 at the skin level. Conclusion There appears to be a relationship between cutaneous T-cell lymphoma and the cutaneous and intestinal microbiome, as well as a possible pathophysiological pathway involved. The possible modulation of the cutaneous and intestinal microbiome or the action on the signaling inflammatory pathway, using pharmacological tools such as JAK inhibitors or IL-17 inhibitors in the latter case, could open the possibility for future therapeutic studies for cutaneous T-cell lymphoma.


Introduction
Cutaneous T-cell lymphoma (CTCL) is a heterogeneous group of non-Hodgkin lymphomas that originate from skinhoming T-cells and manifest as various skin lesions.CTCL is a rare disease with an incidence of 0.5-1 per 100,000 people per year.Te most common subtypes of CTCL are mycosis fungoides (MF) and Sézary syndrome (SS), which account for about 60% and 5% of cases, respectively.Other less common subtypes include primary cutaneous anaplastic large cell lymphoma (pcALCL) and lymphomatoid papulosis (LyP), which belong to the spectrum of CD30-positive lymphoproliferative disorders [1].
Te etiopathogenesis of CTCL remains incompletely understood, but it is likely infuenced by a combination of factors, including genetic mutations, immune dysregulation, environmental exposures, and microbial infections [1,2].One hypothesis regarding the pathogenesis of CTCL suggests that it arises from antigenic stimulation in genetically susceptible individuals [2,3], with evidence indicating that MF may develop in the context of chronic infammation [2][3][4].Specifc HLA alleles have been implicated in an increased risk of developing MF and may afect prognosis, such as HLA-DQB1 * 05, which is associated with the poorest prognosis [5].
In recent years, the role of the human microbiota has gained increasing attention as a contributing factor to CTCL.Te microbiota, comprised of microorganisms inhabiting various body sites including the skin, gut, oral cavity, and genital tract, interacts with the host immune system, infuencing its development and function.Dysbiosis, an imbalance in the composition or function of the microbiota, has been associated with a range of infammatory and neoplastic diseases, further highlighting the potential connection between the microbiota and CTCL [5].Several studies have suggested that dysbiosis may play a role in the pathogenesis or prognosis of CTCL.Some of these studies have reported alterations in the skin microbiota of patients with MF or SS when compared to healthy controls or patients with other dermatoses [6][7][8].Other studies have found association between gut microbiota dysbiosis and systemic infammation or immune suppression in patients with CTCL [9].Moreover, some studies have explored the potential therapeutic efects of modulating the microbiota in CTCL, such as using antibiotics [10][11][12].However, the evidence on this topic is still scarce, inconsistent, and limited by methodological issues.Te aim of this systematic review is to summarize the current literature on the relationship between human microbiota and CTCL, focusing on its etiopathogenic implications and possible new therapeutic targets.

Methods
Tis systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [13].

Search Strategy.
From January 2013 to March 2023, we searched the following electronic databases: MEDLINE (PubMed), Embase, Te Cochrane Library, and Scopus.We used a combination of controlled vocabulary terms and freetext words related to "lymphoma, T-cell, cutaneous," "microbiota," "Mycosis Fungoides," "Sézary Syndrome," "lymphoma, primary cutaneous anaplastic large cell," "Lymphomatoid Papulosis" and "Microbiota," "microbiome," "Microbial Community," and "Microbial Communities."We also applied a flter for human studies.Te detailed search strategy for each database is provided in Figure 1.We also screened the reference lists of the included studies and relevant reviews for additional articles.

Study Selection.
One reviewer screened the titles and abstracts of the retrieved records for eligibility.Discrepancies were resolved by discussion or by consulting a second and third reviewer.Te full texts of potentially eligible articles were obtained and assessed for inclusion by the same three reviewers.Te reasons for the exclusion of full text articles were recorded.

Inclusion Criteria.
We included original research articles that met the following criteria: (i) reported data on human microbiota (skin, gut, or other body sites) in patients with CTCL (any subtype) or healthy controls; (ii) used molecular methods (such as 16S rRNA gene sequencing or metagenomics) to characterize the microbiota; (iii) provided quantitative or qualitative results on microbiota composition, diversity, or function; and (iv) published in English or Spanish.

Exclusion Criteria.
We excluded articles that met any of the following criteria: (i) not original research articles (such as reviews, editorials, or case reports); (ii)used only culture-based methods to characterize the microbiota; (iii) did not provide sufcient data on microbiota analysis; and (iv) were duplicates or overlapping publications.

Study Selection.
Te fow diagram of the study selection process appears in Figure 1.A total of 87 records were identifed from the database searches.After removing 12 duplicates, 75 records were screened by title and abstract.Of these, 31 records were excluded for not meeting the inclusion criteria.Te full texts of the remaining 44 records were assessed for eligibility.Among these, 23 records were further excluded for various reasons (see exclusion criteria).Finally, 21 studies (see Table 1) were included in this systematic review.

Study Characteristics.
Te main characteristics of the included studies are summarized in Table 1.Tese studies were published between 2013 and 2022, with most of them (n � 14) published after 2019.Most articles have focused on Staphylococcus aureus and its pathogenic explanation in patients with cutaneous T-cell lymphoma, with an emphasis on classic mycosis fungoides and Sézary syndrome.Other studies explored the potential application of antibiotic therapy or antiseptics as targeted treatments for cutaneous T-cell lymphoma.Additional articles investigated the cutaneous microbiome and the diferences between lesional and nonlesional skin.Finally, one article examined the diferences in gut microbiota between patients with T-cell lymphoma and healthy individuals.2) refers to the relative abundance of different microbial taxa at various levels of resolution such as phylum, class, order, family, genus, or species.Most studies reported diferences in microbiota composition between patients with CTCL and healthy controls or other comparators [14][15][16][17].However, the results were inconsistent across studies, and no clear patterns emerged [18].Salava et al. [3] investigated the skin microbiome of 20 patients diagnosed with stage IA-IIB mycosis fungoides using 16S rRNA and whole-genome sequencing on skin swab samples.Control samples were collected from healthylooking skin on the opposite side of the same individual.Te study did not fnd any signifcant diferences in microbial diversity or at the genus level.Tough in WGS data analysis, the authors noted a higher abundance of Staphylococcus argenteus in lesional skin, further investigation showed this observation to be inaccurate.Nonetheless, the study did reveal ten bacterial species (Streptomyces sp.SM17, Bordetella pertussis, Streptomyces sp.PVA 94-07, Methylobacterium oryzae, Serratia sp.LS-1, Burkholderia mallei, Enterobacteriaceae bacterium, Achromobacter ruhlandii, Pseudomonas sp.A214, and Pseudomonas sp.st29) that was more abundant in nonlesional skin.
Harkins et al. [4] collected samples from the nares, lower back, and thigh skin (sites of CTCL predilection) using premoistened swabs, as well as air controls.Tese samples were analyzed through shotgun metagenomic sequencing.
Te study found no signifcant diferences in the abundance of viruses and fungi between lesional samples and healthy volunteers, or between Mycosis Fungoides and Sézary Syndrome patients.However, they found higher relative abundances of Corynebacterium spp.and lower relative abundances of Cutibacterium spp. in CTCL patients.
Dehner et al. [2] utilized 16S rRNA gene sequencing to analyze skin swab samples and observed the presence of Bacillus safensis, a rare human skin commensal found only in individuals with diagnosed CTCL, in skin swabs collected from lesional skin of the extremities of CTCL patients but not in other samples.Tey also isolated T-cells and tested the cytokine concentration and proliferative response to different bacteria, fnding that only B. safensis stimulated the proliferation of T-cells.
Zhang et al. [1] utilized 16S rRNA gene sequencing to analyze skin swab samples and found no signifcant differences in bacterial diversity and richness between lesional and nonlesional skin.However, they observed higher abundance of Corynebacterium spp.and Neisseriaceae in lesional skin, whereas nonlesional samples were characterized by an increased abundance of Sandaracinobacter spp.and Enhydrobacter spp.Tey also found microbiome alterations depending on the disease phenotype, with an increase in Staphylococcus spp.observed in patients with marked erythema and a decrease in Propionibacterium spp.and Bradyrhizobium spp. in thickened skin.Painful lesions were associated with decreased Propionibacterium spp.,    [6] studied the efect of ultraviolet light on the skin microbiome in lesioned (LS) and nonlesioned (NLS) skin of patients with CTCL, revealing that UV exposure alters the abundance of certain bacteria in both lesioned and nonlesioned skin.In summary, the data shows that UV exposure returns the microbial communities of lesioned skin to a more normal-like state in responsive patients, while in nonresponsive patients; the skin displays signs of ongoing dysbiosis.
Staphylococcus aureus and its enterotoxin (Figure 2) induce activation of JAK-STAT3 and JAK-STAT5 induces a regulatory T-cell (Treg) phenotype through increased expression of the pro-oncogene FOXP3 [23].Tis phenotype releases IL-10 and TGF-β, promoting immunotolerance.Furthermore, the hyperactivation of miR-155 by STAT5 contributes to a TH2 phenotype [24], which, through its cytokines (IL-4, IL-5, and IL-13), inhibits the TH1 response [22,24], preventing an adequate defense of the organism against the tumor.On the other hand, STAT3 promotes a T17 response with the release of IL-17 and IL-22, perpetuating chronic infammation [25,26].Also, chronic infammation promotes an increase in chromosomal aberrations that enhance the activity of STAT3 and STAT5, or alterations leading to the progression of the lymphoma, such as TP3, MYC, and PTEN [20,23].
Lindahl et al. [16] observed an improvement in skin condition after treatment with intravenous antibiotics (cephalosporins and metronidazole) in patients with stage IIB CTCL.Interestingly, they also noted a decrease in cell proliferation and expression of interleukin-2 receptor (IL2R)-a and tyrosine-phosphorylated STAT3 (pYSTAT3) in immunohistochemical staining after treatment [12].However, long-term use of antibiotics in CTCL patients can promote the development of resistant strains of S. aureus, leading to greater challenges in future eradication eforts.Terefore, long-term antibiotic therapy should only be considered in selected patients and not used daily [12].Another proposed treatment regimen, the Duvic regimen, consisting of intravenous vancomycin and cefepime combined with antiseptic whirlpool baths and corticosteroids with alternating topical antibiotics, resulted in signifcant improvements in the skin condition of patients with erythrodermic CTCL and S. aureus colonization [7,10].
Genetic methods for bacterial identifcation remain expensive, and standard bacterial cultures could be a useful tool for identifying individuals who require antibiotics.Patients with CTCL could also beneft from nonantibiotic therapies to eradicate bacterial colonization.Bleach baths have been found to be a helpful treatment option for patients with atopic dermatitis, with lower S. aureus abundance observed and improvements in skin condition following S. aureus eradication [10,12].Further studies are needed to determine the efectiveness of bleach baths on the skin microbiome in other disease entities.

Gut Microbioma.
Only one study focusing on gut microbiota was included in our systematic review.Hooper et al. [9] investigated the gut microbial profles of 38 patients with cutaneous T-cell lymphoma (CTCL) and 13 healthy individuals using 16S rRNA gene amplicon sequencing.Te results indicated that bacterial dysbiosis was more pronounced in CTCL patients with advanced disease.Te study is signifcant because it is the frst to characterize the gut microbiome in CTCL and is one of the largest sample sets for this disease.Notably, the study found that certain bacterial populations, including Coriobacteriaceae, Lactobacillus, and Bifdobacterium, which were reduced in CTCL patients, have been shown to have benefcial efects in the gut.Bacteria from the family Coriobacteriaceae are known to strengthen gut barrier function, species from the genus Lactobacillus are capable of cytokine-based anti-infammatory activity, and species from the genus Bifdobacterium may promote daily colonic epithelial renewal.In addition, the study found that the presence of Ruminococcaceae was inversely correlated with IL-6 and C-reactive protein levels.
Te study also noted that the dysbiotic signatures observed in CTCL, as well as other malignancies such as psoriasis, may be explained by the complex interactions between the gut microbiome and the immune system.Certain bacterial populations, such as Prevotellaceae and Bacteroidaceae, have been shown to promote local and distant T17 diferentiation and subsequent IL-17 release, which may contribute to CTCL pathogenesis.Te study also found that the loss of butyrate-producing species and enrichment of lipopolysaccharide-secreting species have been linked to tumor proliferation, and that CTCL samples were associated with the loss of butyrate producers and Proteobacteria dysbiosis.

Discussion
Tis systematic review aimed to summarize the current evidence on the human microbiota in patients with cutaneous T-cell lymphoma (CTCL) compared to healthy controls or other comparators.We included 21 studies [6-12, 14-17, 19-28] that analyzed the microbiota from diferent body sites using molecular methods.Te principal fnding is that there is no clear consensus on the microbiota's association with CTCL, with most studies focusing almost exclusively on mycosis fungoides (MF) and Sézary syndrome (SS).Te observed discrepancies can be attributed to the 6 Dermatology Research and Practice heterogeneity of study designs, including variations in sample size, sampling sites, sequencing methods, bioinformatics pipelines, and statistical analyses.Moreover, most of the studies were cross-sectional and observational, which limits the causal inference and generalizability of the results.Terefore, more standardized and rigorous studies are needed to establish a reliable and reproducible microbiota profle for patients with CTCL.Cutaneous microbiota composition, diversity, and function were diferentially altered in patients with CTCL type MF and SS, which could play a role in their development, but the results were inconsistent and conficting across studies [14][15][16][17][18]. Tere is substantial evidence supporting the association between Staphylococcus aureus and on MF and SS.Te efect of antibiotics on the colonization of S. aureus in patients with on MF and SS has been studied, with positive clinical outcomes observed after antibiotic treatment [29][30][31].Talpur et al. [31] identifed S. aureus colonization in patients with MF and SS, and subsequent treatment with dicloxacillin, nafcillin, ampicillin, cephalexin, or clindamycin resulted in negative skin cultures in 30 out of 33 patients after four to eight weeks.Tere is some evidence on the usefulness of antibiotics and antiseptics for MF and SS clinical improvements, as well as improvements in various severity markers of MF and SS [10][11][12]27].
Gut dysbiosis has been linked to cancer and infammatory skin diseases.Research has revealed the tumorigenic potential of certain bacterial taxa and their potent immunomodulatory capabilities [32].Tis suggests that intestinal dysbiosis might both encourage and refect more severe immune dysfunction.It is also understood that intestinal dysbiosis contributes to systemic disease through cytokine-induced infammation, abnormal activation of efector T-cells, and disruptions in the intestinal epithelial barrier that lead to bacterial translocation from the intestinal lumen [33][34][35].Although Hooper et al. [9] provide preliminary evidence suggesting that the gut microbiota may be implicated in on MF and SS; we cannot draw defnitive conclusions at this time due to the limitations of this single, preliminary study.Some of its limitations include a small patient population, heterogeneity among patients, and the fact that, although patients who had received antibiotic therapy within the last month were excluded, we cannot rule out the possibility of permanent changes in the gut microbiome resulting from antibiotic therapy prior to that exclusion period.Terefore, it is necessary to conduct further studies with larger, more homogeneous patient populations and comparison groups, considering any antibiotic therapy received.Adapted from [23][24][25][26].

Dermatology Research and Practice
Te interaction between tumor cells and the microenvironment infuences the progression of MF and SS.In earlystage MF, neoplastic cells are scarce, and reactive helper Tlymphocytes (T1) and CD8+ T-lymphocytes contribute to antitumor defense [2][3][4].As disease progresses, the tumor microenvironment shifts from a T1 to a T2 response, contributing to tumor cell growth and immune escape [2,36].
Tis review pinpoints towards the role of the microbiota in CTCL and towards new insights into the etiology, diagnosis, prognosis, and therapy of CTCL.Some of these insights are: there is potential to use JAK-STAT inhibitors to block their overactivity in cutaneous T-cell lymphoma [39].IL-17 has been implicated in the early and intermediate stages of this lymphoma, where it contributes to chronic infammation and epidermotropism, making it a possible target for therapy [26]; the microbiota may serve as a biomarker for early detection or risk stratifcation of MF and SS [7,9,10,12,27]; the microbiota may be a target for novel therapeutic interventions such as probiotics, prebiotics, symbiotic, or fecal transplantation [9]; the microbiota may be a modifer for existing treatments such as chemotherapy, immunotherapy, or phototherapy [7,9,10,12,19,27].However, these possibilities need to be validated by further research before they can be translated into clinical practice.

Conclusion
Although studies on the composition of the cutaneous and gut microbiota in CTCL patients have shown inconsistent and varied results, it seems that microbial dysbiosis plays a role in the disease, particularly in cases of mycosis fungoides and Sézary syndrome, with insufcient research conducted on other types of cutaneous T-cells.Te relationship between Staphylococcus aureus and mycosis fungoides progression is a promising area of research, and antibiotic treatments might ofer clinical improvements in the skin of afected patients.However, more studies are needed to fully understand the interaction between the

Figure 1 :
Figure 1: PRISMA fow diagram of the study selection process for the systematic review and meta-analysis of cutaneous T-cell lymphoma and microbiota.Te diagram shows the number of records identifed, screened, included, and excluded at each stage of the review, as well as the reasons for exclusion.Adapted from PRISMA fow diagram.

Table 1 : 8 Fujii
Articles included in the systematic review of cutaneous T-cell lymphoma and microbiota. .TCL-036: Alternations in the Skin Microbiota Are Associated with Symptom Severity in Mycosis Fungoides Skin microbiota alterations are linked to symptom severity in mycosis fungoides 16 Dehner et al.Skin Microbiota as Antigenic Triggers for Cutaneous T Cell Lymphoma Skin microbiota may act as antigenic triggers for CTCL 14 Salava et al.Skin Microbiome in Cutaneous T-Cell Lymphoma by 16S and Whole-Genome Shotgun Sequencing Investigated skin microbiome in CTCL using 16S and whole-genome shotgun sequencing 15 Harkins et al.Cutaneous T-Cell Lymphoma Skin Microbiome Characterized by Shifts in Certain Commensal Bacteria CTCL skin microbiome shows shifts in certain commensal bacteria compared to healthy controls 10 Lewis Cutaneous microbiota in the pathogenesis of cutaneous T-cell lymphoma and role of antibiotic therapy Explores the role of cutaneous microbiota and antibiotic therapy in CTCL pathogenesis 19 Hooper et al.Skin microbiome in cutaneous T-cell lymphoma associated with phototherapy treatment response Skin microbiome in CTCL is linked to phototherapy treatment response 25 Wu & Hwang A Microbiota-Dependent, STAT3-Driven Mouse Model of Cutaneous T-Cell Lymphoma Describes a microbiota-dependent, STAT3-driven mouse model of CTCL 37 Fanok et al.Analysis of molecular etiology and bacterial triggers of cutaneous T-cell lymphoma Investigates molecular etiology and bacterial triggers of CTCL 6 Kadin et al.Evidence linking atopy and staphylococcal superantigens to lymphomatoid papulosis pathogenesis Links atopy and staphylococcal superantigens to lymphomatoid papulosis pathogenesis 9 Hooper et al.Gut dysbiosis in CTCL characterized by shifts in bacterial taxa and decreased diversity Gut dysbiosis in CTCL shows shifts in bacterial taxa and decreased diversity in advanced disease 7 Emge et al.MRSA is an important pathogen in erythrodermic CTCL patients MRSA plays a signifcant role in erythrodermic CTCL patients Pathogenesis of cutaneous T-cell lymphoma: Involvement of Staphylococcus aureus Staphylococcus aureus involvement in CTCL pathogenesis 20 Fanok et al.Role of Dysregulated Cytokine Signaling and Bacterial Triggers in CTCL Pathogenesis Dysregulated cytokine signaling and bacterial triggers play a role in CTCL pathogenesis 21 Krejsgaard et al.Staphylococcal enterotoxins stimulate lymphoma-associated immune dysregulation Staphylococcal enterotoxins contribute to lymphoma-associated immune dysregulation 22 Blümel et al.Staphylococcus aureusalpha-toxin inhibits CD8 (+) T-cell-mediated killing of cancer cells in CTCL S. aureusalpha-toxin hinders CD8 (+) T-cell-mediated killing of cancer cells in CTCL 27 Lindahl et al.Staphylococcus aureus and Antibiotics in Cutaneous T-Cell Lymphoma S. aureus and antibiotics' role in CTCL 23 Willerslev-Olsen et al.Staphylococcus aureus enterotoxins induce FOXP3 in neoplastic T-cells in Sézary syndrome S. aureus enterotoxins induce FOXP3 expression in neoplastic T-cells in Sézary syndrome 24 Willerslev-Olsen et al.Staphylococcus aureus Induces STAT5-Dependent miR-155 Expression in Cutaneous T-Cell Lymphoma S. aureus induces STAT5-dependent miR-155 expression in CTCL 11 Lewis et al.Te "Duvic Regimen" for Erythrodermic Flares Secondary to Staphylococcus aureus in Mycosis Fungoides Describes the "Duvic Regimen" for treating erythrodermic fares caused by S. aureus in mycosis fungoides 26 Willerslev-Olsen et al.Staphylococcal enterotoxin A (SEA) stimulates STAT3 activation and IL-17 expression in CTCL SEA activates STAT3 and induces IL-17 expression in CTCL 12 Lindahl et al.Antibiotics inhibit tumor activity and disease in cutaneous T-cell lymphoma Antibiotics inhibit tumor activity and disease progression in CTCL 4 Dermatology Research and Practice

Figure 2 :
Figure 2: Efects of Staphylococcus aureus and its enterotoxin on the immune response in cutaneous T-cell lymphoma.Te fgure illustrates how the bacterial infection and its toxin activate JAK-STAT3 and JAK-STAT5 pathways, leading to the generation of regulatory T cells (Treg), TH2 cells, and T17 cells, which suppress the antitumor immunity and promote chronic infammation and genomic instability.Adapted from[23][24][25][26].

Table 2 :
Summary of articles describing the cutaneous microbiota in patients with cutaneous T-cell lymphoma (CTCL).Te table shows the main fndings and methods of each study.Study Bradyrhizobium spp., and Staphylococcus spp.Excoriation was characterized by reduced Conchiformibus spp., and pruritus was associated with an increase in Sphingomonas spp.and Parvimonas spp.Hooper et al.